1. Field of the Invention
The present invention relates to a seal device. Particularly, it relates to a seal device provided with a lip seal which is brought into slidable contact with a rotary shaft at an outer circumference thereof.
2. Background of the Invention
Conventionally, a seal device provided with a lip seal for slidably contacting a rotary shaft has been known. An example of such a seal device comprises a casing surrounding a circumference of a rotary shaft, a seal member attached to the casing, and a lip seal sandwiched at its outer circumferential portion between the seal member and a spacer supported by the casing. The lip seal is in slidable contact at its inner circumferential surface with an outer circumferential surface of the rotary shaft to thereby seal the contacting portion therebetween (Japanese Patent Publication No. 721/1967, see FIG. 8 thereof).
In the case where the lip seal is sandwiched between the seal member and the spacer, however, the lip seal can be securely sandwiched in comparison with the case where the seal member is omitted. As a result, a sealed fluid which is apt to leak through a gap between the spacer and the lip seal and through a gap between the lip seal and the seal member can be effectively prevented from leaking. However, when the seal member ages, its elasticity is reduced due to its long use or the like. As a result, the lip seal is often rotated as the rotary shaft rotates due to a frictional force between the lip seal and the rotary shaft. The rotation of the lip seal sometimes allows the sealed fluid to leak out through a gap between the lip seal and the seal member.